1. Field of the Invention
The present invention is directed to an implantable defibrillator of the type having a capacitor which is connectable via a controllable switch arrangement to a voltage source for charging or to electrodes placed at the heart for delivery of defibrillation pulses thereto, and to a method for inducing fibrillation using such a defibrillator.
2. Description of the Prior Art
In known implantable defibrillators, a capacitor connected within the implantable defibrillator housing or capsule, is charged to a high voltage via a voltage source, also in the housing, and is subsequently discharged through electrodes arranged at the heart and via the heart tissue lying between the electrodes, upon the detection of ventricular fibrillation. A controllable switch arrangement normally connects the capacitor across a voltage source for charging the capacitor, and alternatively connects the capacitor across the electrodes when defibrillation is necessary. When the current flowing across the heart has sufficient energy, ventricular fibrillation is thereby terminated.
In order to identify the minimum amount of energy which is sufficient to achieve a successful defibrillation, it is known to induce ventricular fibrillation artificially, and subsequently to implement a series of defibrillation attempts with increasing energy until the ventricular fibrillation is successfully terminated. For example, ventricular fibrillation can be induced by externally charging the patient with a 50 Hz alternating current from an external generator. It is possible to artificially produce ventricular fibrillation by generating a suitable stimulation pulse sequence by means of a heart pacemaker, which may be implanted either separately from the implantable defibrillator, or in combination with the defibrillator in a common housing.